Project Summary Molecular and cellular determinants of Drosophila larva thermotaxis How nervous systems detect and integrate multiple sensory cues to generate robust behaviors is a major question in neuroscience. Such integration is particularly salient in thermosensing, as animals are frequently required to integrate input from multiple thermoreceptor classes. Temperature's ubiquity also means input from other modalities (e.g., olfaction) is commonly received in the context of ongoing thermosensory stimulation. Achieving a comprehensive understanding of the molecular and circuit mechanisms underlying the integration of information from multiple sensors remains a challenge. We will address this challenge in the Drosophila larva. Its ease of genetic manipulation, synaptic-resolution connectome of thermosensory and olfactory processing areas, amenability to neuronal imaging, and stereotyped behaviors, all make it a favorable system for a comprehensive molecular and circuit level investigation of the mechanisms of sensory integration. We propose to achieve these goals in three aims: Aim 1) Establish the molecular and cellular receptors that provide thermosensory input In aims 1.a. and 1.b., we will identify the molecular basis of thermosensing by thermosensory neurons in the larval Dorsal Organ and examine their roles in guiding behavior through cell-specific inhibition and activation combined with high-resolution behavioral analysis. Aim 2) Probe the activities of the interneurons that process thermosensory input In aim 2.a., we will examine how thermosensory inputs act to modulate the neuronal activity of individually identifiable downstream projection neurons revealed from the larval antennal lobe connectome. This will establish the manner in which peripheral sensory input influences these second-order interneurons. In aim 2.b., we will investigate how thermosensory and olfactory systems interact in multi-sensory integration of chemical and thermal cues. Aim 3) Probe the functions of the interneurons that process thermosensory input In aim 3, we will determine the contribution of each projection neuron to thermotactic navigation through cell- specific inhibition and activation of individual PNs combined with high-resolution behavioral analysis. Taken together, these studies combine molecular genetics, physiology, and high resolution behavioral analyses to perform a comprehensive analysis of how this relatively small neural circuit processes multiple, distinct sensory inputs to control robust and flexible behaviors.